Memory that retains its data even when operation power is not available is classified as nonvolatile memory. Examples of non-volatile memory are nvSRAM, F-RAM, electrically erasable programmable read-only memory (EEPROM), and flash memories. This class of memory may be used in applications in which critical data must be stored after power is removed, or when power is interrupted during operation.
Reference voltage for a memory device or cell may be interpreted as a voltage level that separates what is to be considered a data value “0” or a “1” stored, depending on the charge stored/generated in the memory device or cell. In certain embodiments, voltages found on the memory bus below the reference voltage are to be considered a “0” and voltages above the reference voltage are to be considered a “1”, or vice versa. In some embodiments, the reference voltage may be kept at a constant level, programmable, or a combination thereof.
In some non-volatile memory devices, such as F-RAM devices, the charge output from ferroelectric capacitors, such as the switching and non-switching terms, may be temperature dependent. Therefore, there are advantages to have the reference voltage programmable or variable such that more accurate read operation of such F-RAM devices may be attainable.